Semiconductor device including fin structure with two channel layers and manufacturing method thereof

ABSTRACT

A method for manufacturing a semiconductor device includes forming a fin structure having a top face and a first side face and a second side face opposite to the first side face, forming a lower cover layer over the first and second side faces, forming an upper cover layer over the first and second side faces, the upper cover layer being spaced apart from the lower cover layer so that exposed regions of the first and second side faces are formed between the lower cover layer and the upper cover layer, and forming first and second semiconductor layers over the exposed regions of the first and second side faces, respectively.

CROSS-CITATION TO RELATED APPLICATIONS

This application is a Divisional Application of U.S. Ser. No. 14/604,537 filed Jan. 23, 2015, the subject matter of which is incorporated by reference in entirety.

TECHNICAL FIELD

The disclosure relates to a semiconductor integrated circuit, more particularly to a semiconductor device having a fin structure and its manufacturing process.

BACKGROUND

As the semiconductor industry has progressed into nanometer technology process nodes in pursuit of higher device density, higher performance, and lower costs, challenges from both fabrication and design issues have resulted in the development of three-dimensional designs, such as a fin field effect transistor (Fin FET). Fin FET devices typically include semiconductor fins with high aspect ratios and in which channel and source/drain regions of semiconductor transistor devices are formed. A gate is formed over and along the sides of the fin devices (e.g., wrapping) utilizing the advantage of the increased surface area of the channel and source/drain regions to produce faster, more reliable and better-controlled semiconductor transistor devices. In addition, strained materials in source/drain (S/D) portions of the Fin FET utilizing selectively grown silicon germanium (SiGe) may be used to enhance carrier mobility. For example, compressive stress applied to a channel of a PMOS device advantageously enhances hole mobility in the channel. Similarly, tensile stress applied to a channel of an NMOS device advantageously enhances electron mobility in the channel.

However, there are challenges to implementation of such features and processes in complementary metal-oxide-semiconductor (CMOS) fabrication.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale and are used for illustration purposes only. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is an exemplary perspective view of a semiconductor FET device having a fin structure (Fin FET) according to one embodiment of the present disclosure;

FIG. 2 is an exemplary plan view of the semiconductor device having a fin structure;

FIG. 3 is an exemplary cross sectional view along the line X1-X1′ of FIG. 2;

FIG. 4 is an exemplary cross sectional view along the line X2-X2′ of FIG. 2;

FIG. 5 is an exemplary cross sectional view along the line Y-Y′ of FIG. 2;

FIGS. 6-11 show is exemplary cross sectional views of channel layers according to some embodiments of the present disclosure;

FIGS. 12-29 show exemplary processes for manufacturing the Fin FET device according to one embodiment of the present disclosure;

FIGS. 30 and 31 show exemplary processes for manufacturing the Fin FET device according to another embodiment of the present disclosure;

FIGS. 32-35 show exemplary processes for manufacturing the Fin FET device according to yet another embodiment of the present disclosure; and

FIGS. 36-39 show exemplary processes for manufacturing the Fin FET device according to another embodiment of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific embodiments or examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, dimensions of elements are not limited to the disclosed range or values, but may depend upon process conditions and/or desired properties of the device. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. Various features may be arbitrarily drawn in different scales for simplicity and clarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. In addition, the term “made of” may mean either “comprising” or “consisting of.”

FIG. 1 shows an exemplary perspective view of the Fin FET device according to one embodiment of the present disclosure. FIG. 2 is an exemplary plan view of the Fin FET according to one embodiment of the present disclosure. In FIG. 2, only one fin structure is illustrated. FIG. 3 is an exemplary cross sectional view along the line X1-X1′ of FIG. 2, FIG. 4 is an exemplary cross sectional view along the line X2-X2′ of FIG. 2, and FIG. 5 is an exemplary cross sectional view along the line Y-Y′ of FIG. 2. In these figures, some layers/features are omitted for simplification.

The Fin FET device 1 includes, among other features, a substrate 10, a fin structure 20, channel layers 30, a gate dielectric 80 (shown in FIG. 5) and a gate electrode 40. In this embodiment, the substrate 10 is a silicon substrate. Alternatively, the substrate 10 may comprise another elementary semiconductor, such as germanium; a compound semiconductor including IV-IV compound semiconductors such as SiC and SiGe, III-V compound semiconductors such as GaAs, GaP, GaN, InP, InAs, InSb, GaAsP, AlGaN, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinations thereof. In one embodiment, the substrate 10 is a silicon layer of an SOI (silicon-on insulator) substrate. When an SOI substrate is used, the fin structure may protrude from the silicon layer of the SOI substrate or may protrude from the insulator layer of the SOI substrate. In the latter case, the silicon layer of the SOI substrate is used to form the fin structure. Amorphous substrates such as amorphous Si or amorphous SiC, or insulating material such as silicon oxide may also be used as the substrate 10. The substrate 10 may include various regions that have been suitably doped with impurities (e.g., p-type or n-type conductivity).

The fin structure 20 is disposed over the substrate. The fin structure 20 may be made of the same material as the substrate 10 and may continuously extend from the substrate 10. In this embodiment, the fin structure is made of Si. The silicon layer of the fin structure 20 may be intrinsic, or doped with an n-type impurity or a p-type impurity. In this embodiment, the silicon layer of the fin structure is intrinsic.

In FIG. 1, three fin structures 20 are disposed over the substrate 10. However, the number of the fin structures is not limited to three. The numbers may be one, two or four or more. In addition, one of more dummy fin structures may be disposed at both sides of the fin structures 20 to improve pattern fidelity in patterning processes. The width of the fin structure 20 is in a range of about 5 nm to about 40 nm in some embodiments. The height of the fin structure 20 is in a range of about 10 nm to about 50 nm in some embodiments, and may be in a range of about 20 nm to 30 nm in other embodiments.

The lower part of the fin structure 20 is covered by a lower cover layer 45. The lower cover layer 45 is disposed over side faces (side walls) of the fin structure 20 and also disposed over the substrate 10. In some embodiments, the lower cover layer 45 includes a first liner layer 50 and a second liner layer 60 disposed over the first liner layer 50. The first liner layer 50 may be a silicon oxide liner layer and the second liner layer 60 may be a silicon nitride liner layer in some embodiments. The thickness of the first liner layer 50 is in a range of about 1 nm to about 15 nm in some embodiments. The thickness of the second liner layer 60 is in a range of about 1 nm to about 25 nm.

The upper part of the fin structure 20 is covered by an upper cover layer 70. The upper cover layer 70 is disposed over the side faces of the fin structure and also disposed over the top surface of the fin structure 20. In this embodiment, the upper cover layer 70 includes a silicon nitride layer. In some embodiments, the upper cover layer may be multiple layers including a first layer and a second layer disposed over the first layer, where the first layer may be a silicon oxide layer and the second layer may be a silicon nitride layer. The lower cover layer 45 and the upper cover layer 70 are spaced apart from each other. In some embodiments, the upper cover layer 70 is over the fin structure covered by the gate electrode 40 and is not over the fin structure not covered by the gate electrode 40, or the upper cover layer may not exist over the fin structure 20. The thickness of the upper cover layer 70 is in a range of about 1 nm to about 15 nm.

Channel layers 30 are disposed over both side faces of the fin structure 20 in the space between the lower cover layer 45 and the upper cover layer 70. The height T1 (vertical length, see. FIG. 5) of the channel layer 30 is smaller than a height of the fin structure 20. The channel layer 30 includes a Ge layer in some embodiments. In other embodiments, the channel layer 30 may include a stacked layer of, in the order closer to the side face of the fin structure, Ge, Si, Si/Ge, Si/Si_((1-x))Ge_(x)/Ge, Si/Si_((1-x))Ge_(x) or Si_((1-x))Ge_(x)/Ge, where x may be about 0.15 or more and less than 1 in some embodiments. The channel layer 30 may be made by epitaxial silicon formed on silicon fin structure in certain embodiments. The thickness W1 (horizontal length, see. FIG. 5) of the channel layer 30 is in a range of about 5 nm to about 30 nm in some embodiments. The height T1 of the channel layer 30 is in a range of about 5 nm to about 120 nm in some embodiments.

Since two channel layers 30 are disposed per one fin structure, the number of channels is double compared with a case where one channel is formed on one fin structure.

As shown in FIG. 5, a gate electrode 40 is disposed over the fin structure so as to cover the channel layers 30. A gate dielectric layer 80 is interposed between the gate electrode 40 and the channel layer 30. The gate dielectric layer 80 is also disposed over the upper cover layer 70. The gate electrode 40, the gate dielectric layer 80 and the channel layers 30 constitute two MOS FETs. The two MOS FETs may be the same type (p/n) or different types, and the two channel layers 30 may be electrically coupled with each other. Part of the channel layer 35 not covered by the gate electrode 40 functions as a source and/or drain of the MOS FETs.

In certain embodiments, the gate dielectric layer 80 includes a dielectric material, such as silicon oxide, silicon nitride, or high-k dielectric material, other suitable dielectric material, and/or combinations thereof. Examples of high-k dielectric material include HfO₂, HfSiO, HfSiON, HfTaO, HfTiO, HfZrO, zirconium oxide, aluminum oxide, titanium oxide, hafnium dioxide-alumina (HfO₂—Al₂O₃) alloy, other suitable high-k dielectric materials, and/or combinations thereof.

The gate electrode 40 includes any suitable material, such as polysilicon, aluminum, copper, titanium, tantalum, tungsten, cobalt, molybdenum, tantalum nitride, nickel silicide, cobalt silicide, TiN, WN, TiAl, TiAlN, TaCN, TaC, TaSiN, metal alloys, other suitable materials, and/or combinations thereof. The gate structure may be formed using a gate-last or replacement gate methodology.

In certain embodiments of the present disclosure, work function adjustment layers (not shown) may be interposed between the gate dielectric layer 80 and the gate electrode 40. The work function adjustment layer may include a single layer or alternatively a multi-layer structure, such as various combinations of a metal layer with a selected work function to enhance the device performance (work function metal layer), liner layer, wetting layer, adhesion layer, metal alloy or metal silicide. The work function adjustment layers are made of a conductive material such as a single layer of Ti, Ag, Al, TiAlN, TaC, TaCN, TaSiN, Mn, Zr, TiN, TaN, Ru, Mo, Al, WN, Cu, W, Re, Jr, Co, Ni, other suitable metal materials, or a multilayer of two or more of these materials. In some embodiments, the work function adjustment layer may include a first metal material for the n-channel Fin FET and a second metal material for the p-channel Fin FET. For example, the first metal material for the n-channel Fin FET may include metals having a work function substantially aligned with a work function of the substrate conduction band, or at least substantially aligned with a work function of the conduction band of the channel layer 30. Similarly, for example, the second metal material for the p-channel Fin FET may include metals having a work function substantially aligned with a work function of the substrate valence band, or at least substantially aligned with a work function of the valence band of the channel layer 30. In some embodiments, the work function adjustment layer may alternately include a polysilicon layer. The work function adjustment layer may be formed by ALD, PVD, CVD, e-beam evaporation, or other suitable process. Further, the work function adjustment layer may be formed separately for the n-channel Fin FET and the p-channel Fin FET which may use different metal layers.

Source and drain regions 35 are also formed in the Ge channel layer 30 not covered by the gate electrode 40, by appropriately doping impurities in the source and drain regions 35. An alloy of Ge or Si and a metal such as Co, Ni, W, Ti or Ta may be formed on the source and drain regions 35.

Further, spaces between the fin structures and/or a space between one fin structure and another element formed over the substrate 10 are filled by shallow-trench-isolation (STI) oxide including an insulating material. The insulating material for the STI may include silicon oxide, silicon nitride, silicon oxynitride (SiON), SiOCN, fluoride-doped silicate glass (FSG), or a low-K dielectric material.

The structure of the channel layer 30 is not limited to the structure shown in FIG. 1 or 5. FIGS. 6-11 show exemplary cross sectional views of channel layers according to other embodiments of the present disclosure. In FIGS. 6-11, some features, for example, the first liner layer 50, the second liner layer 60, upper cover layer 70 and gate dielectric layer 80, are not shown for simplicity.

In certain embodiments, as shown in FIG. 6, the channel layer 30 includes a Si layer 34 disposed over the side face of the fin structure 20 and a Ge layer 32 disposed over the Si layer 34. The Si layer 34 is an epitaxial Si layer and the Ge layer 32 is also an epitaxial Ge layer in some embodiments.

In certain embodiments, as shown in FIG. 7, the channel layer 30 includes a Si layer 34 disposed over the side face of the fin structure 20, a Si_((1-x))Ge_(x) layer 36 disposed over the Si layer 34 and a Ge layer 32 disposed over the Si_((1-x))Ge_(x) layer 36. The Si layer 34 is an epitaxial Si layer, the Si_((1-x))Ge_(x) layer 36 is an epitaxial Si_((1-x))Ge_(x) layer, and the Ge layer 32 is also an epitaxial Ge layer in some embodiments. The value of x is in a range of about 0.15 or more and less than 1.0 in some embodiments.

In some embodiments, the channel layer 30 may include, from the side face of the fin structure, Si, Ge/Si, Si_((1-x))Ge_(x)/Si, Ge/Si_((1-x))Ge_(x)/Si or Si_((1-x))Ge_(x)/Ge/Si. The channel layer 30 may be made by epitaxial silicon formed on silicon fin structure in certain embodiments.

As shown in FIG. 8, corners of the channel layer 30 may have a rounded shape in some embodiments. Further, as shown in FIG. 9, the end portion of the channel layer 30 may have a rounded shape. Similar to FIGS. 6 and 7, the stacked layer of the Si layer 34 and the Ge layer 32 or the stacked layer of the Si layer 34, the Si_((1-x))Ge_(x) layer 36 and the Ge layer 32 may be applicable to the channel layer having rounded corners and/or rounded end portion. For example, as shown in FIG. 10, the channel layer 30 includes a Si layer 34 disposed over the side face of the fin structure 20 and a Ge layer 32 disposed over the Si layer 34, and the corners of the Ge layer 32 are rounded. As shown in FIG. 11, the channel layer 30 includes a Si layer 34 disposed over the side face of the fin structure 20, a Si_((1-x))Ge_(x) layer 36 disposed over the Si layer 34 and a Ge layer 32 disposed over the Si_((1-x))Ge_(x) layer 36, and the corners of the Ge layer 32 are rounded. The rounded corners and/or end portion of the channel layer 30 may relax electric field concentration at the corner of the channel layer.

FIGS. 12-24 show cross sectional views of exemplary sequential processes of the Fin FET device according to one embodiment. It is understood that additional operations can be provided before, during, and after processes shown by FIGS. 12-24, and some of the operation described below can be replaced or eliminated, for additional embodiments of the method. The order of the operations/processes may be interchangeable.

As shown in FIG. 12, a mask layer 100 is formed over the substrate 10 by, for example, a thermal oxidation process and/or a chemical vapor deposition (CVD) process. The substrate 10 is, for example, a silicon substrate. The mask layer 100 includes, for example, a pad oxide (e.g., silicon oxide) layer 105 and a silicon nitride mask layer 110 in some embodiments. The thickness of the pad oxide layer 105 is in a range of about 2 nm to about 15 nm and the thickness of the silicon nitride mask layer 110 is in a range of about 2 nm to about 50 nm in some embodiments. A mask pattern 120 is further formed over the mask layer 100. The mask pattern 120 is, for example, a photo resist pattern formed by photo lithography.

By using the mask pattern 120 as an etching mask, hard mask pattern of the pad oxide layer 105 and the silicon nitride mask layer 100 are formed. The width of the hard mask pattern is in a range of about 5 nm to about 40 nm in some embodiments. In certain embodiments, the width of the hard mask patterns is in a range of about 5 nm to about 30 nm.

As shown in FIG. 13, by using the hard mask pattern as an etching mask, the substrate 10 is pattered into fin structures 20 by trench etching using a dry etching method and/or a wet etching method. A height D1 of the fin structure 20 is in a range of about 30 nm to about 300 nm. In certain embodiments, the height D1 is in a range of about 30 nm to about 200 nm. When the heights of the fin structures are not uniform, the height D1 from the substrate may be measured from the plane that corresponds to the average heights of the fin structures.

In this embodiment, a bulk silicon wafer is used as a starting material and constitutes the substrate 10. However, in some embodiment, other types of substrate may be used as the substrate 10. For example, a silicon-on-insulator (SOI) wafer may be used as a starting material, and the insulator layer of the SOI wafer constitutes the substrate 10 and the silicon layer of the SOI wafer is used for the fin structure 20.

As shown in FIG. 14, a cover layer 45 is formed over the fin structure 20 by, for example, a thermal oxidation process and/or a CVD process. The cover layer 45 includes, for example, an oxide (e.g., silicon oxide) cover layer 50 and a silicon nitride (SiN) cover layer 60 in some embodiments. The oxide cover layer 50 may be formed by, for example, a thermal oxidation process on the side walls of the fin structures 20. Then, the SiN cover layer 60 may be formed by a CVD process. Other film forming methods can be applied in forming the oxide cover layer 50 and/or the SiN cover layer 60. The thickness of the oxide cover layer 50 is in a range of about 1 nm to about 15 nm and the thickness of the silicon nitride cover layer 60 is in a range of about 1 nm to about 25 nm in some embodiments.

The SiN cover layer 60 may be deposited by physical vapor deposition (PVD) (sputtering), CVD, plasma-enhanced chemical vapor deposition (PECVD), atmospheric pressure chemical vapor deposition (APCVD), low-pressure CVD (LPCVD), high density plasma CVD (HDPCVD), atomic layer deposition (ALD), and/or other processes. In a LPCVD process, a silicon source such as Si₂H₆, SiH₄ and/or Si₂Cl₆ and a nitrogen source such as NH₃ and/or N₂ are used and the SiN film is formed at a temperature in a range of about 900-1200° C. under a reduced pressure in a range of about 0.01 to 10 Torr (about 1.33 Pa to about 1333 Pa) in some embodiments. In a plasma CVD process, the process temperature is in a range of 250-500° C.

As shown in FIG. 15, a sacrificial layer 130 is formed so that the fin structures are embedded in the sacrificial layer 130. The fin structures 20 may be fully or partially embedded in the sacrificial layer 130. In this embodiment, the sacrificial layer is a photo resist layer. The photo resist layer is formed by spin coating. The photo resist layer may be replaced with any organic resin (e.g., non-photosensitive resins) layer or inorganic layer. A material for a bottom anti-reflection coating may be used.

Then, as shown in FIG. 16, the thickness of the sacrificial layer 130 is reduced by, for example, an etch-back process so as to expose a part of the fin structures. The etch-back process of the photo resist may be performed by using plasma including O₂ and at least one of CF₄ and CHF₃, at a temperature in a range about 0° C. to about 300° C. and at a pressure in a range of about 1 to about 10 Torr (about 133 Pa to about 1333 Pa) in certain embodiments. By adjusting etching time, a desired thickness of the remaining photo resist layer can be obtained. The remaining thickness T2 is adjusted to a range of about 10 nm to about 150 nm in some embodiments.

Instead of etching-back the thick resist layer, it may be possible to form a thin sacrificial layer of the photo resist having the thickness T2 directly by adjusting, for example, the spin coating condition.

Next, as shown in FIG. 17, part of the silicon nitride cover layer 60 exposed from the sacrificial layer 130 is removed by plasma etching or wet etching.

The remaining sacrificial layer 130 is removed by, for example, an ashing process and/or a wet cleaning process, as shown in FIG. 18.

As shown in FIG. 19, an isolation insulating layer 140 is formed. The fin structures 20 may be fully or partially embedded in the isolation insulating layer 140. The isolation insulating layer 140 is made of, for example, silicon dioxide formed by LPCVD (low pressure chemical vapor deposition), plasma-CVD or flowable CVD. In the flowable CVD, flowable dielectric materials instead of silicon oxide are deposited. Flowable dielectric materials, as their name suggest, can “flow” during deposition to fill gaps or spaces with a high aspect ratio. Usually, various chemistries are added to silicon-containing precursors to allow the deposited film to flow. In some embodiments, nitrogen hydride bonds are added. Examples of flowable dielectric precursors, particularly flowable silicon oxide precursors, include a silicate, a siloxane, a methyl SilsesQuioxane (MSQ), a hydrogen SilsesQuioxane(HSQ), an MSQ/HSQ, a perhydrosilazane (TCPS), a perhydro-polysilazane (PSZ), a tetraethyl orthosilicate (TEOS), or a silyl-amine, such as trisilylamine (TSA). These flowable silicon oxide materials are formed in a multiple-operation process. After the flowable film is deposited, it is cured and then annealed to remove un-desired element(s) to form silicon oxide. When the un-desired element(s) is removed, the flowable film densifies and shrinks. In some embodiments, multiple anneal processes are conducted. The flowable film is cured and annealed more than once at temperatures, such as in a range from about 1000° C. to about 1200° C., and for an extended period, such as 30 hours or more in total. The isolation insulating layer 140 may be formed by SOG. SiO, SiON, SiOCN or fluoride-doped silicate glass (FSG) may be used as the isolation insulating layer in some embodiments. After forming the isolation insulating layer 140, a thermal process, for example, an anneal process, may be performed to improve the quality of the isolation insulating layer.

As shown in FIG. 20, part of the isolation layer 140 is removed by, for example, a chemical mechanical polishing (CMP) method or other planarization methods such as an etch-back process, so that the top surface of the silicon nitride mask layer 110 is exposed. The top portions of the silicon nitride mask layer 110 may be slightly etched.

As shown in FIG. 21, the silicon nitride mask layer 110 is removed, by wet etching and/or dry etching process. The pad oxide layer 105 is also removed.

As shown FIG. 22, a silicon nitride (SiN) layer 115 is formed. The SiN layer 115 may be formed by a CVD process similar to the SiN cover layer 60 as explained above. The thickness of the SiN layer 115 is in a range of about 2 nm to about 15 nm in some embodiments.

As shown in FIG. 23, a planarization operation is performed to remove the unnecessary portions of the SiN layer 115 and the isolation layer 140 so that SiN layer 115 remains only on the top surface of the fin structure 20. The thickness of the remaining SiN layer 115 after the planarization operation is in a range of about 2 nm to about 8 nm in some embodiments.

As shown in FIG. 24, the thickness of the isolation insulating layer 140 is reduced by, for example, an etch-back process so as to expose a part of the fin structure 20. The etch-back process may be performed by using dry etching or wet etching. By adjusting etching time, a desired thickness of the remaining insulating layer 140 can be obtained. In the present disclosure, the thickness T3 is adjusted to be in a range of about 15 nm to about 270 nm in some embodiments. Here, T3 is about T1+T2. In this process, the silicon oxide layer 60 at the tope portion of the fin structure 20 is also removed.

As shown in FIG. 25, another silicon nitride (SiN) layer 117 is formed. The SiN layer 117 may be formed by a CVD process similar to the SiN cover layer 60 as explained above. The thickness of the SiN layer 117 is in a range of about 1 nm to about 15 nm in some embodiments.

As shown in FIG. 26, an etch-back process is performed to remove unnecessary portion of the SiN layer 117 so that an upper cover layer 70 is formed over the upper portion of the fin structure 20. The thickness of the resultant upper cover layer 70 is in a range of about 2 nm to about 40 nm in some embodiments. The thickness of upper cover layer 70 is not limited to this range and may depend upon the etching condition or other process factors.

As shown in FIG. 27, the thickness of the remaining isolation insulating layer 140 is further reduced by, for example, an etch-back process so as to expose a center part 25 of the fin structure 20, which is not covered by the SiN cover layer 60 and the upper cover layer 70. The etch-back process may be performed by using dry etching or wet etching. By adjusting etching time, a desired thickness of the remaining isolation insulating layer 140 can be obtained. In the present disclosure, the thickness T4 of the remaining isolation insulating layer 140 is adjusted to be in a range of about 10 nm to about 100 nm in some embodiments. T4 is smaller than T2. In some embodiments, the isolation insulating layer 140 may be fully removed. In this process, the silicon oxide layer 60 in the center part 25 is also removed, and the lower cover layer 45 is obtained.

A shown in FIG. 28, channel layers 30 are formed over the exposed portion 25 of the fin structure 20. The channel layer 30 may be a Ge layer, a stacked layer of Si and Ge or a stacked layer of Si, Si_((1-x))Ge_(x) and Ge, or even a Si layer, as explained with respect to FIGS. 6-11.

When the channel layer 30 is made of Ge, the Ge layer is epitaxially grown on the exposed portion 25 by using, for example, GeH₄ and/or Ge₂H₆ as source gas at a temperature in a range of about 300° C. to about 500° C. and at a pressure in a range of about 10 Torr to about 500 Torr.

The Si_((1-x))Ge_(x) layer may be epitaxially grown by using, for example, SiH₂Cl₂ and/or SiH₄ and GeH₄ and/or Ge₂H₆ as source gas at a temperature in a range of about 500° C. to about 700° C. and at a pressure in a range of about 10 Torr to about 100 Torr. The value of x may be constant in the Si_((1-x))Ge_(x) layer or may increase in the Si_((1-x))Ge_(x) layer as being grown. The Si layer may also be epitaxially grown by using, for example, SiH₂Cl₂ and/or SiH₄ as source gas at a temperature in a range of about 600° C. to about 800° C. and at a pressure in a range of about 10 Torr to about 100 Torr. The channel layer 30 may appropriately be doped with, for example, boron and/or phosphorous in an amount of about 1×10¹⁹ to 5×10¹⁹ cm⁻³, in some embodiments.

As shown in FIG. 29, the gate structure is formed over the fin structure 20 with the channel layers 30.

The gate dielectric layer 80 is formed by CVD, PVD, ALD e-beam evaporation, or other suitable process. When the gate dielectric layer 80 is silicon oxide, SiH₄, Si₂H₆ and/or Si₂Cl₆ is used as a source gas. When the gate dielectric layer 80 is silicon nitride, SiH₄, Si₂H₆ and/or Si₂Cl₆ and NH₃ are used as source gases. When the gate dielectric layer 80 is hafnium oxide, zirconium oxide, aluminum oxide or titanium oxide, metal hydride, metal chloride and/or organic metal including Hf, Zr, Al or Ti is used as a source gas.

The gate electrode 40 may be formed by a film forming process by using ALD, PVD, CVD, e-beam evaporation, electroplating or other suitable process, and a patterning process. Metal hydride, metal chloride and/or organic metal including Ti, Ta, Co, Si, Zr, Al or W is used as a source gas. The gate structure may be formed using a gate-last or replacement gate methodology.

FIGS. 30 and 31 show cross sectional views of another exemplary sequential process of the Fin FET device according to one embodiment.

After the channel layers 30 are formed as shown in FIG. 28, a plasma treatment is performed on the channel layer 30 so that the corners and/or the end portion of the channel layer 30 are rounded as shown in FIG. 30. Then, as shown in FIG. 31, the gate structure is formed over the fin structure 20 with the rounded channel layers 30.

FIGS. 32-35 show exemplary processes for manufacturing the Fin FET device according to yet another embodiment of the present disclosure.

After the process shown in FIG. 26, portion of the SiN cap layer 70 disposed over the upper surface of the fin structure 20 is removed, by for example, a CMP process so that the upper surface 27 of the fin structure 20 is exposed, as shown in FIG. 32.

Similar to FIG. 27, the thickness of the remaining isolation insulating layer 140 is further reduced by, for example, an etch-back process so as to expose a center part 25 of the fin structure 20, which is not covered by the SiN cover layer 60 and the upper cover layer 72, as shown in FIG. 33.

A shown in FIG. 34, channel layers 30 and a third channel layer 32 are formed over the exposed portion 25 and exposed upper surface 27 of the fin structure 20, similar to FIG. 28. The channel layers 30 and 32 may be a Ge layer, a stacked layer of Si and Ge or a stacked layer of Si, Si_((1-x))Ge_(x) and Ge, as explained with respect to FIGS. 6-11. The dimension Wc1 of the channel layers 30 and the dimension Wc2 of the third channel layer 32 may be the same or different, the conduction type of the third channel 32 may be the same as or different from the conduction type of the channel layer 30.

As shown in FIG. 35, the gate structure including gate electrode 40 and gate dielectric layer 80 is formed similar to FIG. 29, thereby forming a three-channel MOS Fin FET.

FIGS. 36-39 show exemplary processes for manufacturing the Fin FET device according to another embodiment of the present disclosure.

In the process shown in FIG. 23, the SiN layer 115 is removed from the top surface of the fin structure 20. The SiN layer 115 may slightly be remained. Then, the process shown in FIG. 24 is performed to reduce the height of the isolation layer 140. After these processes, a cap layer 74 is formed over the fin structure 20 and interlayer insulating layer 140, as shown in FIG. 36.

In the alternative, as shown in FIG. 38, after the process shown in FIG. 19, the hard mask patterns formed by the oxide layer 105 and the nitride layer 110 and top portions of the isolation insulating layers 140 are removed by, for example, a chemical mechanical polishing (CMP) method or other planarization methods such as an etch-back process. The top portions of the fin structure 20 may be slightly etched.

As shown in FIG. 39, the thickness of the isolation insulating layer 140 is reduced by, for example, an etch-back process so as to expose a part of the fin structure 20. The etch-back process may be performed by using dry etching or wet etching. By adjusting etching time, a desired thickness of the remaining insulating layer 140 can be obtained. In the present disclosure, the thickness T3 is adjusted to be in a range of about 15 nm to about 270 nm in some embodiments. In this process, the silicon oxide layer 60 at the tope portion of the fin structure 20 is also removed. After the process shown in FIG. 39, a cap layer 74 is formed over the fin structure 20 and interlayer insulating layer 140, as shown in FIG. 36.

By using an etching process such as a plasma dry etching, side walls 76 are formed so that the upper surface 27 of the fin structure 20 is exposed, as shown in FIG. 37. Then, the channel layer 30 and third channel layer 32 are formed similar to FIG. 34, and the gate structure is further formed similar to FIG. 35, thereby forming a three-channel MOS Fin FET.

The various embodiments or examples described herein offer several advantages over the existing art. For example, in the present disclosure, since two channel layers including a Ge layer are disposed per one fin structure, the number of channels is double compared with a case where one channel is formed on one fin structure, and therefore a high density of high speed transistor using a Ge channel can be obtained.

It will be understood that not all advantages have been necessarily discussed herein, no particular advantage is required for all embodiments or examples, and other embodiments or examples may offer different advantages.

In accordance with one aspect of the present disclosure, a semiconductor device includes a fin structure for a fin field effect transistor (FET). The semiconductor device includes a fin structure protruding from a substrate and having a top face and a first side face and a second side face opposite to the first side face, and first semiconductor layers disposed over the first and second side faces of the fin structure. The thickness in a vertical direction of the first semiconductor layers is smaller than a height of the fin structure.

In accordance with another aspect of the present disclosure, a semiconductor device includes a fin structure for a fin field effect transistor (FET). The semiconductor device includes a fin structure protruding from a substrate and having a top face and a first side face and a second side face opposite to the first side face, first semiconductor layers disposed over the first and second side faces of the fin structure, and a second semiconductor layer disposed over the top face of the fin structure.

In accordance with another aspect of the present disclosure, a method for manufacturing a semiconductor device includes the following operations. A fin structure having a top face and a first side face and a second side face opposite to the first side face is formed. A lower cover layer is formed over the first and second side faces. An upper cover layer is formed over the first and second side faces. The upper cover layer is spaced apart from the lower cover layer so that exposed regions of the first and second side faces are formed between the lower cover layer and the upper cover layer. First semiconductor layers are formed over the exposed regions of the first and second side faces, respectively.

The foregoing outlines features of several embodiments or examples so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments or examples introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method for manufacturing a semiconductor device, comprising: forming a fin structure having a top face and a first side face and a second side face opposite to the first side face; forming a lower cover layer over the first and second side faces; forming an upper cover layer over the first and second side faces, the upper cover layer being spaced apart from the lower cover layer so that exposed regions of the first and second side faces are formed between the lower cover layer and the upper cover layer; and forming first and second semiconductor layers over the exposed regions of the first and second side faces, respectively.
 2. The method of claim 1, wherein the forming a lower cover layer comprises: forming a liner layer to cover the first and second side faces of the fin structure; forming a sacrificial layer to cover a part of the liner layer so that a remaining part of the liner layer is exposed from the sacrificial layer; and removing the exposed liner layer.
 3. The method of claim 1, wherein the forming a lower cover layer comprises: forming a liner layer to cover the first and second side faces of the fin structure; forming a sacrificial layer to cover the liner layer; removing a part of the sacrificial layer so that a remaining part of the liner layer is exposed; and removing the exposed liner layer.
 4. The method of claim 1, wherein the forming an upper cover layer comprises: forming an insulating layer to cover a part of the first and second side faces so that a remaining part of the first and second side faces, which is not covered by the lower cover layer, is exposed from the insulating layer; forming a cap layer to cover the exposed part of the first and second side faces; and removing at least a part of the insulating layer so that the exposed regions of the first and second side faces are exposed from the insulating layer.
 5. The method of claim 1, wherein the forming an upper cover layer comprises: forming an insulating layer to cover the fin structure with the lower cover layer; removing a part of the insulating layer so that a part of the first and second side faces which is not covered by the lower cover layer is exposed; forming a cap layer to cover the exposed part of the first and second side faces; and removing at least a part of the insulating layer so that the exposed regions of the first and second side faces are formed.
 6. The method of claim 1, wherein the lower cover layer and the upper cover layer include a silicon nitride layer.
 7. The method of claim 1, wherein the forming first and second semiconductor layers comprises: forming first and second silicon layers over the exposed regions of the first and second side faces, respectively; and forming first and second Ge including layers over the first silicon layer and the second silicon layer, respectively.
 8. The method of claim 1, further comprising: rounding end portions of the first and second semiconductor layers.
 9. The method of claim 1, further comprising: forming a gate dielectric layer over the first and second semiconductor layers; and forming a gate electrode over the gate dielectric layer.
 10. A method for manufacturing a semiconductor device, comprising: forming a fin structure having a top face and a first side face and a second side face opposite to the first side face; forming a lower cover layer over the first and second side faces; forming an upper cover layer over the first and second side faces, the upper cover layer not covering the top surface of the fin structure and being spaced apart from the lower cover layer so that exposed regions of the first and second side faces are formed between the lower cover layer and the upper cover layer; and forming first and second semiconductor layers over the exposed regions of the first and second side faces, respectively, and a third semiconductor layer over the top surface of the fin structure.
 11. The method of claim 10, wherein the forming a lower cover layer comprises: forming a liner layer to cover the first and second side faces of the fin structure; forming a sacrificial layer to cover a part of the liner layer so that a remaining part of the liner layer is exposed from the sacrificial layer; and removing the exposed liner layer.
 12. The method of claim 10, wherein the forming a lower cover layer comprises: forming a liner layer to cover the first and second side faces of the fin structure; forming a sacrificial layer to cover the liner layer; removing a part of the sacrificial layer so that a remaining part of the liner layer is exposed; and removing the exposed liner layer.
 13. The method of claim 10, wherein the forming an upper cover layer comprises: forming an insulating layer to cover a part of the first and second side faces so that a remaining part of the first and second side faces, which is not covered by the lower cover layer, is exposed from the insulating layer; forming a cap layer to cover the top face and the exposed part of the first and second side faces; removing a portion of the cap layer covering the top surface so as to expose the top surface; and removing at least a part of the insulating layer so that the exposed regions of the first and second side faces are exposed from the insulating layer.
 14. The method of claim 10, wherein the forming an upper cover layer comprises: forming an insulating layer to cover the fin structure with the lower cover layer; removing a part of the insulating layer so that a part of the first and second side faces which is not covered by the lower cover layer is exposed; forming a cap layer to cover the exposed part of the first and second side faces; and removing at least a part of the insulating layer so that the exposed regions of the first and second side faces are formed.
 15. The method of claim 10, wherein the first through third semiconductor layers include a same material.
 16. The method of claim 10, wherein the forming first through third semiconductor layers comprises: forming first and second silicon layers over the exposed regions of the first and second side faces, respectively, and a third silicon layer over the top surface; and forming first through third Ge including layers over the first through third silicon layers, respectively.
 17. A method for manufacturing a semiconductor device, comprising: forming a plurality of fin structures each having a top face and a first side face and a second side face opposite to the first side face, the plurality of fin structures arranged parallel to each other; forming a lower cover layer over the first and second side faces of each of the plurality of fin structures; forming an upper cover layer over the first and second side faces of each of the plurality of fin structures, the upper cover layer being spaced apart from the lower cover layer so that exposed regions of the first and second side faces are formed in each of the plurality of fin structures between the lower cover layer and the upper cover layer of each of the plurality of fin structures; and forming first and second semiconductor layers over the exposed regions of the first and second side faces, respectively, such that one of the first and second semiconductor layers of a first one of the plurality of fin structures and one of the first and second semiconductor layers of a second one of the plurality of fin structures protrude toward each other from the first fin structure and the second fin structure, respectively.
 18. The method of claim 17, further comprising: removing portions of the upper cover layers covering the top surfaces of the plurality of fin structures; and forming third semiconductor layers over the top surfaces of the plurality of fin structures.
 19. The method of claim 18, wherein the first through third semiconductor layers include a same material.
 20. The method of claim 17, wherein the forming first and second semiconductor layers comprises: forming first and second silicon layers over the exposed regions of the first and second side faces, respectively, of each of the plurality of fin structures; and forming first and second Ge including layers over the first silicon layer and the second silicon layer, respectively, of each of the plurality of fin structures. 